The invention relates to a process for the manufacturing of a double-walled hollow lost casing having plane inner and outer surfaces, to be used in the production of marine engineering civil works, such as pier, a jetty, a reservoir etc. said lost casing being made with inner and outer walls of sheets which are pre cut to size and shape beforehand such that the lost casing in each horizontal section is inwardly and outwardly polygonal and at least in the lower part of the casing has outwardly and downwardly sloping inner and outer walls respectively, which form a sharp bottom edge.
Such a process can be deduced from the international patent application WO NO. 87/03026, laid open for inspection. This application describes a lost casing for the manufacturing of e.g. a pier or a jetty which comprises an inner wall and an outer wall, which both in each horizontal section have the shape of a polygon whilst the outer wall at least in the lower region flares downwardly and outwardly and forms with the inner wall, which also has a downwardly and outwardly widening portion, a sharp bottom edge. This casing is manufactured from steel plates which are welded upon one another at their edges with transverse connecting members between inner and outer wall plates. This hollow steel casing can be provided with reinforcing rods and at a suitable moment during the manufacturing of e.g. a pier can be filled with concrete to form a rigid column.
The manufacturing of such a lost casing can be further improved in order to speed up the production, in particular when the casings serve to manufacture columns or other elements of large dimensions in the vertical direction as well as in the horizontal direction. With large dimensions rigidity and support is necessary during the manufacturing because the not yet finished casing has no inherent stability.